WDPN31 PGTW 160300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (VONGFONG) WARNING
NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 01W (VONGFONG), LOCATED APPROXIMATELY 212
NM NORTH-NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED NORTH-
NORTHWESTWARD AT 21 KNOTS OVER THE PAST SIX HOURS. THE INITIAL
POSITION IS PLACED WITH GOOD CONFIDENCE BASED ON ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI), WHICH SHOWS AN EXPOSED LOW-
LEVEL CIRCULATION CENTER (LLCC) JUST OFFSHORE THE WEST COAST OF
LUZON, WITH FLARING DEEP CONVECTION WELL REMOVED TO THE EAST. THE
INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON A 152218Z WINDSAT
PASS AND A BLEND OF DVORAK ANALYSES FROM PGTW AND RJTD OF T3.0 AND
T2.0, RESPECTIVELY. POLEWARD OUTFLOW REMAINS GOOD AHEAD OF AN
APPROACHING MID-LATITUDE TROUGH, SEA SURFACE TEMPERATURES (SST) ARE
WARM (30-31 DEGREES CELSIUS), AND VERTICAL WIND SHEAR IS MODERATE
(15-20 KNOTS) BUT INCREASING. TS 01W IS TRACKING AROUND THE
WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
A. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE FORECAST
PHILOSOPHY.
B. TS 01W IS FORECAST TO TRACK NORTHWARD ALONG THE WESTERN
PERIPHERY OF THE STEERING STR THROUGH TAU 12, FOLLOWED BY A TURN
TOWARD THE NORTHEAST. AN UPPER-LEVEL MID-LATITUDE TROUGH IS
APPROACHING FROM THE NORTHWEST, WHICH WILL ERODE THE STR BEYOND TAU
24. THIS WILL ALLOW TS 01W TO TURN TOWARD THE NORTHEAST AND
ACCELERATE, WITH GOOD AGREEMENT AMONG THE DYNAMICAL MODEL GUIDANCE.
GIVEN THAT MUCH OF ITS CIRCULATION HAS DECOUPLED, TS 01W IS FORECAST
TO CONTINUE TO WEAKEN, ESPECIALLY GIVEN THE INCREASED VERTICAL WIND
SHEAR AHEAD OF THE APPROACHING TROUGH. BEYOND TAU 36, TS 01W WILL
ACCELERATE AND BEGIN TO DISSIPATE OVER WATER AS IT IS ABSORBED BY
THE BAROCLINIC ZONE. EXTRATROPICAL TRANSITION IS NOT EXPECTED DURING
THIS PERIOD, GIVEN THE DECOUPLED STRUCTURE OF TS 01W AND WEAK UPPER-
LEVEL DYNAMICS. TS 01W IS FORECAST TO DISSIPATE BY TAU 48. GIVEN THE
TIGHT CLUSTERING IN DYNAMICAL MODEL GUIDANCE, THERE IS HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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